Detection, quantification, isolation and purification of target biomaterials, such as microbes and biomacromolecules (including constituents or products of living cells, for example, proteins, carbohydrates, lipids, and nucleic acids) have long been objectives of investigators. Detection and quantification are important diagnostically, for example, as indicators of various physiological conditions such as diseases. Isolation and purification of biological targets are important for therapeutic uses and in biomedical research. Biomolecules such as enzymes which are a special class of proteins capable of catalyzing chemical reactions are also useful industrially.
In their native state in vivo, structures and corresponding biological activities of biomolecules are maintained generally within fairly narrow ranges of pH and ionic strength. Consequently, any separation and purification operation must take such factors into account in order for the resultant, processed biomacromolecule to have potency.
Chromatographic separation and purification operations have become the primary method for the isolation of biological molecules in the biopharmaceutical industry. Most current chromatography is done via conventional column techniques, and are operated in either bind-and-elute (e.g., when the target species is the object of purification) or in flow-through mode (e.g., when the target species if a contaminant to be removed). These techniques have severe bottlenecking issues in downstream purification, as the throughput using this technology is low. Attempts to alleviate these issues include increasing the diameter of the chromatography column, but this in turn creates challenges due to difficulties of packing the columns effectively and reproducibly. Larger column diameters also increase the occurrence of problematic channeling. Also, in a conventional chromatographic column, the adsorption operation is shut down when a breakthrough of the desired product above a specific level is detected. This causes the dynamic or effective capacity of the adsorption media to be significantly less than the overall or static capacity. This reduction in effectiveness has severe economic consequences, given the high cost of some chromatographic resins.
Membrane chromatography has the potential to offer significant advantages over column chromatography for the separation of biomaterials, especially biomolecules, due to the convective nature of the fluid flow through the material. With the polymeric resins widely used for column chromatography, pore diffusion must also occur in order for the target molecule to interact with its binding site, dramatically increasing the processing time needed for the separation operation. The main problems with utilization of membrane chromatography for large-scale purifications, however, have been the lack of good techniques for functionalization of the membranes and generally the low binding capacities for target species. Thus, there is a need in the art for polymeric substrates, especially membranes, having enhanced affinity for microbes and other biological species to allow selective removal from a biological sample. There is further need in the art for ligand functionalized substrates that overcome limitations in diffusion and binding, and that may be operated at high throughput and at lower pressure drops.